In conventional furnaces and processes for the production of sponge iron, a hydrocarbon is mixed with exhaust gas recovered from the furnace and a mixture is reacted (converted) at certain temperatures and generally in the presence of a catalyst, to the reducing gas. The conversion or reformation involves a partial combustion of the hydrocarbon.
The reformation can also take place in regenerators or cowpers which are heated partially or completely by exhaust gas from the furnace or by other means.
All of the conventional processes described above require low-carbon hydrocarbons, such as methane and natural gas, as the energy carrier. Hence conventional processes are limited to the use of hydrocarbons which are free from sulfur since otherwise sulfur in the form of hydrogen sulfide or carbonyl sulfide becomes entrained with the reducing gas and is picked up by the sponge iron.
When steel of high quality is to be made, sulfur-containing sponge iron cannot be used or must be subjected to further treatment to eliminate the sulfur. Such sulfur-removal treatments are highly expensive and energy-consuming.